The petcock(drain) for the radiator will be at the bottom on the drivers' side, and look like a big plastic wingnut! I've found by placing a homeade 2 liter bottle funnel with a length of hose on it makes less of a mess draining the coolant into a container. If you don't, it tends to run down the framerail! When I did my truck, I bought a bottle of radiator flush at the parts store, you drain out your anti-freeze, pour in the flush, add water to fill rad, then run engine with heater on, drain rad, then repeat. This stuff really does the trick! I suggest using Dexcool coolant(Texaco Havoline) if your truck doesn't already use it. I found it at a department store for the same price as regular antifreeze! It lasts for 5 years or 100,000 miles whichever comes first, The only thing to run IMHO if you have anything aluminum in your cooling system!.
Now, as for the fluid levels, I know the rear plug is on the passengers' side, and is an allen head, just like the calipers(3/8 I think). A caliper socket is the best tool to use to check it. I think the front IFS plug is the same as the rear, but its on the front of the housing. I believe its the only plug, so if you ever want to change the 90W, you'd need a suction gun to get it out. The transfer case has a few different plugs, but you want the closest one to the top, I usually use a large crescent wrench to get these. On your transmission, if its a manual, its should have 2 or more plugs on the drivers' side, again you want the highest one(lower ones are drain plugs). If its an auto, drive around until its up to Normal temp, leave engine running and check level on dipstick in park, it should be in the safe area on the dipstick. Well, hope this helps you out and answers your questions.
1989 S10 4x4
1989 SBlazer 4x4